Functional hearing depends on the formation of appropriate connections between neurons in the auditory circuit during development. Axons of cochlear ganglion neurons bifurcate upon reaching the hindbrain in order to distribute information from cochlear hair cells to both divisions of the cochlear nucleus. There, the tonotopic organization of the cochlea is preserved and different features of complex sound stimuli are processed separately. In order to determine the timing and location of axon branching, cochlear ganglion projections will be visualized using genetic techniques in the mouse. Individual projections will be labeled in order to define the sequence of events that occur during branch formation at the single cell level. Further insights into the cellular mechanisms of axon branching will come from live imaging of individual cochlear ganglion axons. To begin to define the relative contributions of intrinsic and extrinsic factors, cochlear and vestibular neurons will be compared for their abilities to branch in isolation or when co- cultured with hindbrain tissue. These studies will contribute significantly to our understanding of the assembly and function of auditory circuits and may reveal novel strategies to promote axon regeneration.